Biomedical subjects

Thomas Wenzl

Publications and source records attributed to Thomas Wenzl.

11 recordsLinked to original sources

PubMed2006

Collaborative trial validation study of two methods, one based on high performance liquid chromatography-tandem mass spectrometry and on gas chromatography-mass spectrometry for the determination of acrylamide in bakery and potato products.

A European inter-laboratory study was conducted to validate two analytical procedures for the determination of acrylamide in bakery ware (crispbreads, biscuits) and potato products (chips), within a concentration range from about 20 microg/kg to about 9000 microgg/kg. The methods are based on gas chromatography-mass spectrometry (GC-MS) of the derivatised analyte and on high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) of native acrylamide. Isotope dilution with isotopically labelled acrylamide was an integral part of both methods. The study was evaluated according to internationally accepted guidelines. The performance of the HPLC-MS/MS method was found to be superior to that of the GC-MS method and to be fit-for-the-purpose.

Acrylamide↗

PubMed2006

Investigation of the correlation of the acrylamide content and the antioxidant activity of model cookies.

The purpose of this study was to evaluate the correlation between the acrylamide (AA) content and the antioxidant activity (AOA) of self-prepared cookies. Cookies were baked in the laboratory under defined conditions following four different recipes. The parameters of investigation were the influence of the type and relative content of sugar (glucose and fructose) and the baking time on the AA content as well as AOA of the final products. Parameters depending on the recipe and baking conditions such as the moisture content, the total nitrogen concentration, and the color of the products were evaluated for all samples as well. To prove the transferability of the findings gained with model cookies to samples from industry, the same measurements were performed on seven different types/brands of cookies that were purchased in local markets. A direct correlation was found between the concentration of AA and the AOA. With increasing baking time, the moisture content of the cookies decreased. The latter parameter correlated well with the AA concentration and AOA. The use of fructose enhanced the concentration of AA and the AOA of the final products, when compared with the use of sucrose. However, a simple model for the prediction of acrylamide contents and the AOA of samples from the baking time, color, protein, or moisture content of the samples was not found.

Acrylamide↗

PubMed2004

Chemometrical classification of pumpkin seed oils using UV-Vis, NIR and FTIR spectra.

The main outcome of this work is elaboration of classification models for edible oil samples representing the most widespread brands of Austrian pumpkin seed oil. A complete spectral characterisation of the pumpkin seed oil samples by UV-Vis, NIR and FTIR spectra was obtained together with their basic sensorial classification. Chemometrical processing of the measured data enabled the detection of the most important spectral features, which are crucial for categorising the oils into two or three classes according to their sensory quality evaluated by a panel of experts. The elaborated models thus make it possible to predict the category into which a hitherto unclassified oil sample belongs--considering classification into either two categories, containing oils with overall acceptable scores or oils that were not accepted, or three categories, involving oils fulfilling all quality criteria, oils with good scores and not accepted oils. This will perspectively facilitate the determination of chemical substances responsible for bad taste, odour and colour of the respective oil brands, as well as finding substances contributing to the excellent sensorial perception of some tested products.

Algorithms↗

PubMed2004

Evaluation of the results from an inter-laboratory comparison study of the determination of acrylamide in crispbread and butter cookies.

Analytical methods currently employed for determination of acrylamide (AA) in two carbohydrate-rich food samples, crispbread and butter cookies, obtained commercially, and native and spiked bread extract samples have been evaluated in a collaborative study. The objective of the study was to obtain information about the performance of the participating laboratories when analysing samples with an AA content close to the limit of quantification ( LOQ) and at a higher AA level, and to investigate the influence of sample-preparation procedures on the results of the analysis. For this purpose an aqueous native extract of white bread crumb, a fortified extract, and AA standard solutions, the analyte content of which were not disclosed to the participants, were included in the study. A total of 62 laboratories, applying seven different measurement techniques and a broad spectrum of analyte extraction and sample-preparation procedures reported their analytical results. Because the measurement data were not normally distributed, they were evaluated by application of robust statistics. The relative performance of the laboratories was highlighted by calculation of z-scores. For the crispbread sample, especially, a large percentage of the calculated z-scores were outside the satisfactory range. From their distribution it became obvious that one of the analytical techniques might be biased, if not applied correctly. Consequently, the impact of the applied methods was examined in more detail. Information about the analytical technique, extraction solvent, quantity weighed, calibration method, clean-up, and the experience of the participating laboratories were extracted from the analytical protocols and transcribed into a data matrix which was evaluated by multifactor analysis of variance. The applied measurement technique seems to have a statistically significant influence on the analytical results.

Journal Article↗

PubMed2002

Triazines in the aquatic systems of the Eastern Chinese Rivers Liao-He and Yangtse.

The results of a one-year monitoring program on the two Eastern Chinese River systems, i.e. the Liao-He and the Yangtse, with special emphasis on the presence of triazine herbicides are presented. Sediment, suspended solids and water samples from both rivers were analyzed. Additionally, recovery experiments on the SPE-in-field-enrichment procedure and the extraction methods were performed. The samples were measured by gas chromatography coupled with mass spectrometry, electron capture detection and a newly developed mu-plasma atomic emission detector. A typical result of a one-year monitoring was obtained in case of the Liao-He: During winter, at low water period, low triazine values were found. A similar situation was found in early spring. Highest concentrations of atrazine up to 1600 ng/l were found in late spring in the water samples. Maximum concentrations of atrazine, simazine, propazine, simetryn and prometryn were observed in this season as a result of the actual use of triazines. Finally, after the high water period in autumn the triazine concentrations decreased. Additionally, atrazine adsorbed on sediment (up to 2.8 ng/g) and suspended solids was determined (up to 8 ng/l) during late spring sampling. Therefore, the logarithm of the organic carbon based sorption coefficient of atrazine could be calculated. Low levels of atrazine were measured in the water of Yangtse (up to 18.3 ng/l). The concentrations from all sampling points and sampling stations of a particular sampling date were similar, which indicates a homogeneous distribution of this herbicide. Due to the high discharge rate of up to 79,000 m3/s in case of the Yangtse a considerable mass transport of up to 57.5 kg per day atrazine may take place, even at concentrations below the European drinking water limit of 100 ng/l.

Adsorption↗

PubMedDate not supplied

Determination and quantification of clonidine in human blood serum.

Clonidine ((2-[2,6-dichlorophenyl]amino)-2-imidazoline) preferentially stimulates central alpha(2)-adrenoceptors, which leads to inhibition of sympathetic tone, resulting in a lowering of arterial pressure and of heart rate. Additionally, many other desirable and undesirable effects are described, including analgesia, sedation and withdrawal reactions, which consist of a sudden rise in arterial pressure, nervousness, agitation and increased heart rate. The present study has the goal to develop a simple and effective method for the analysis of trace amounts of clonidine in human blood serum. Special emphasis is necessary to make application of electron impact ionization and separation of the analyte fragments in a quadruple mass analyzer suitable. The procedure comprises solid phase extraction followed by formation of the pentafluorobenzyl derivative. Further purification is achieved by phase transfer extraction into an acidic aqueous solution succeeded by re-extraction into dichloromethane. After solvent exchange, an aliquot is injected into the gas chromatograph equipped with a DB5 MS capillary column and a mass spectrometric detector. Chromatograms are recorded in single ion monitoring mode. Quantification is accomplished by internal standardization with moxonidine [4-chloro-5-(2-imidazolin-2-yl-amino)-6-methoxy-2-methylpyridine].

Blood Chemical Analysis↗

PubMedDate not supplied

An improved method to discover adulteration of Styrian pumpkin seed oil.

Pumpkin seed oil is rather expensive compared to other vegetable oils. Therefore, it is often adulterated by the addition of cheaper oils. In contrast to other edible oils, the content of Delta 5-sterols is very low, while Delta 7-sterols are dominating. The determination of Delta 5-sterols, especially beta-sitosterol has proven to be a good possibility to detect admixture of cheap vegetable oils to a level below which the economic profit is not significant any more. The presented method is a variant of an analysis concept, which has been published previously in European Food Research and Technology by Mandl et al. [Eur. Food Res. Technol. 209 (1999) 400. ]. It includes saponification of the triglycerides as a first step followed by separation of the potassium salts of the fatty acids from the unsaponifiable fraction by adsorption chromatography. In order to enhance gas chromatographic properties of the analytes, the hydroxyl function of the sterols is derivatized with N-Methyl-N-(trimethylsilyl)trifluoroacetamide (MSTFA) to the trimethylsilylether. Finally, the analytes are separated on a capillary column of medium polarity (HP 35 MS) in a temperature programmed run within 18 min. Detection of the analytes was done by flame ionization. Special attention was set onto the precision and repeatability of the method.

Chromatography↗

PubMedDate not supplied

Occurrence of triazines in surface and drinking water of Liaoning Province in Eastern China.

The Liaoning Province in Eastern China has a prosperous economy and traditional agricultural background. Steadily increasing water demand implies the direct use of surface water for drinking water support and foodstuff production. Due to the extensive use, high persistence, water solubility and relatively weak adsorptivity, the chloro s-triazines contaminate the aquatic environment and are therefore regularly and most frequently detected in ground and surface water. Water sample enrichment procedures were performed by solid-phase extraction (SPE) using different materials. During a 1-year monitoring program on the Liao-He River, water sample enrichment was performed using C(18)-SPE cartridges. These SPE cartridges showed low recoveries for the atrazine metabolites, although high triazine values were detected. Based on these results, a pilot sampling on drinking water in the Liao-He region was performed. This time, in addition to the C(18)-SPE cartridges, a new polymer SPE sorbent made from a balance ratio of two monomers, the lipophilic divinylbenzene and the hydrophilic N-vinylpyrrolidone, was used. Both materials were characterized by establishing breakthrough curves for the investigated analytes and up to large volumes.

China↗

PubMedDate not supplied

Overview of acrylamide monitoring databases.

Since high acrylamide levels in carbohydrate-rich food were reported in 2002, many research activities were started in order to gain knowledge on occurrence, formation, and prevention of this compound in food products. Among them, monitoring programs were conducted in many countries worldwide by official bodies as well as by the food industry. National and international bodies set up monitoring databases. In 2003, both the European Commission and the World Health Organization posted calls for data and placed their spreadsheets for the submission of data on the Web. The goal of the databases is to collect data for a reliable estimation of the exposure of consumers to acrylamide via the food chain. This paper describes the assessment of the data quality and outlines the composition of the data in the 2 databases, to date.

Acrylamide↗

PubMedDate not supplied

Results from two interlaboratory comparison tests organized in Germany and at the EU level for analysis of acrylamide in food.

After the publication of high levels of acrylamide (AA) in food, many research activities started all over the world in order to determine the occurrence and the concentration of this substance in various types of food. As no validated methods were available at that time, interlaboratory studies on the determination of AA in food were of the highest priority. Under the boundary conditions of applying well-established evaluation schemes, the results of 2 studies conducted by the Federal Institute for Risk Assessment (BfR) in Germany and by the European Commission's Directorate General Joint Research Center (JRC) exhibited an overall acceptable performance of the participants in these studies. Nevertheless, many laboratories showed problems in determining AA in food with a complex matrix such as cocoa. The results of analysis also showed a broader variation of AA for samples with low AA concentrations and indicated a bias of the results obtained by gas chromatography-mass spectrometry without derivatization. Improvements of the performance of some laboratories appeared to be necessary.

Acrylamide↗

PubMedDate not supplied

Evaluation of results of an interlaboratory comparison test on determination of acrylamide in crispbread samples.

The European Commission's Directorate General Joint Research Centre has organized several proficiency tests on the determination of acrylamide (AA) in food. This paper presents the results and outcome of a proficiency test that focused on the determination of AA in crispbread samples. One of the goals was the identification of the influence of different parameters such as analyte extraction or instrument calibration on the analytical results. A set of samples, containing 3 different crispbread samples as well as extracts of one crispbread sample and AA standard solutions, was shipped to each participant. A total of 42 European laboratories reported analytical results that were evaluated by applying internationally accepted protocols and procedures. The study found that, for each sample, the results of 4-8 laboratories were outside the range formed by the target value plus or minus the 2-fold of the target standard deviation; thus, they did not perform satisfactorily. In transferring this knowledge to the data of monitoring databases of AA in food, care must be taken that data are quality controlled, as it is likely that some of them may be biased.

Acrylamide↗